Echo processing apparatus

Abstract

An echo canceller has a high-pass filter 11, a speaker 3, an A/D converter 6, and an echo canceller 7. The high-pass filter 11 suppresses a low-frequency component in a received signal. The speaker 3 outputs an acoustic sound of a low-frequency suppressed received signal passed through the high-pass filter 11. The A/D converter 6 converts an acoustic echo from a microphone 4 into a transmission signal of a digital form. The echo canceller 7 generates a pseudo echo signal based on the low-frequency suppressed received signal passed through the high-pass filter 11, and eliminates the acoustic echo to be inputted to the microphone 4 from the speaker 3 by subtracting the pseudo echo signal from the digital signal converted by the A/D converter 6.

Description

TECHNICAL FIELDThe present invention relates to an echo processor for reducing an acoustic echo component outputted from a speaker inputted to a microphone transferred through an echo path in an acoustic communication using mobile units such as an on-vehicle telephone and a cellular phone.BACKGROUND ARTFIG. 1 is a block diagram showing a configuration of a circuit of a conventional echo processor. In the diagram, reference number 1 designates a digital to analogue (D / A) converter for converting a received signal in digital form to a sound signal in analogue form, 2 denotes an amplifier for amplifying the sound signal, and 3 indicates a speaker for outputting the acoustic corresponding to the sound signal amplified. Reference number 4 designates a microphone for inputting an acoustic and converting it to a sound signal, 5 denotes an amplifier for amplifying the sound signal, and 6 indicates an analogue to digital (A / D) converter for converting the amplified sound signal to a digital ...

AI Technical Summary

Benefits of technology

It is thereby possible to extract the low-frequency component in the digital signal with a simple configuration and it is not necessary to replace the current low-pass filter in the double-talk detector with new one according to the change of the cutoff-frequency caused by replacing a kind of the speaker. Thus, it is easily to cope with the change of the cutoff-frequency by rewriting the set-frequency stored in the memory.

Problems solved by technology

In this case, a non-linear distortion occurs in the echo signal inputted through the microphone and the calculation accuracy of the adaptive filter coefficient calculated by the adaptive filter 8 is thereby deteriorated.

Further, there is a drawback in which the difference between the pseudo echo signal to be generated and the echo signal becomes large, and the amount of the echo suppression becomes reduced.

In a case in which a high-pass filter is inserted between the D / A converter and the amplifier at the received signal side, it is difficult to match the frequency components of this high-pass filter and both the high-pass filters placed before the adaptive filter and before the adder because the purpose to suppress the low frequency component is different between those high-pass filters.

As a result, the drawback occurs that the characteristic of the low frequency component is greatly different between the received signal to be inputted to the adaptive filter and the echo signal to be inputted to the microphone, this deteriorates the calculation accuracy of the adaptive filter coefficient and the difference between the pseudo echo signal and the echo signal becomes large, and the amount of the echo suppression is thereby reduced.

Thus, the conventional echo cancellers involve the drawback in which there is a possibility to occur the wrong judgment because it is difficult to distinct the single-talk and the double-talk apparently.

As a result, the wrong judgment to halt and start the update of the adaptive filter coefficient occurs, so that the calculation accuracy of the adaptive filter coefficient is deteriorated and the amount of the echo suppression is thereby reduced.

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